Gelable compositions and use thereof in steam treatment of wells

ABSTRACT

A gelable composition is provided which can be injected into a well prior to steam treatment of the well. The composition comprises water, a water-dispersible polymer, a water-dispersible first crosslinker and a water-dispersible second crosslinker, wherein the first and second crosslinkers have differing temperature responsive crosslinking characteristics over the temperature range of about 70° F. to about 400° F. so as to enable crosslinking of the polymer and gelation of the composition over substantially the entire temperature range. Injection of the composition into a &#34;cold&#34; well followed by steam treatment of the well causes the polymer to undergo a two stage crosslinking reaction which produces a particularly effective and stable gel in diverting steam from &#34;thief zones&#34; in the formation surrounding the well.

This is a divisional of application Ser. No. 006,821, filed Jan. 23,1987.

BACKGROUND OF THE INVENTION

This invention relates to a gelable composition which has differentcrosslinkers therein which crosslink a water-dispersible polymer in thecomposition at corresponding different temperature ranges. In anotheraspect, the invention relates to use of this composition in steamtreatment of wells for enhanced oil recovery.

Steam treatment of wells has been practiced for some time in order toheat especially heavy crudes in a subterranean formation so as to reducethe crude viscosity and enhance oil recovery. Many problems have beenencountered in such steam treatments, however. One problem results fromthe typically varying permeability of different strata in the formation.The injected steam will tend to flow into the more permeable portions(hereafter referred to as "thief zones") of the formation, therebyleaving other possibly oil bearing zones untouched.

Various methods of plugging or sealing off thief zones for divertingsteam into the less permeable zones have been used. One method involvessurfactants which are added to injected steam to form steam foams whichplug or increase the flow resistance of thief zones. The desireddiversion of steam away from thief zones, however, is achieved for onlya short time after the steam injection. As the steam cools andcondenses, the foam tends to collapse and the desired effect is lost.Other chemicals have been proposed for blocking their zones, but few areeconomically attractive or provide good penetration into a formation,and if a permanent blockage of thief zones is desired, few chemicals canwithstand the effects of high steam temperatures over prolonged periods.For example, lignosulfonate forms a gel that can block thief zones, butit loses its effectiveness with prolonged exposure to high temperatures.

In summary, the existing technology of steam diversion from thief zonesis inadequate insofar as prior thief zone sealants are effective inblocking thief zones for an undesirably short period of time after steaminjection, or fail to penetrate deep enough into the formation.

SUMMARY OF THE INVENTION

It is, therefore, an object of the invention to provide compositionswhich can be injected into a well so as to effectively block the thiefzones in the surrounding subterranean formation.

It is also an object of the invention to provide such compositions whichwhen injected provide good penetration into the formation, and which canwithstand the high temperatures associated with the steam injection forextended periods.

The above objects of the invention are satisfied by a composition whichcomprises, and preferably consists essentially of: water; awater-dispersible polymer; a first water-dispersible crosslinker; and asecond water-dispersible crosslinker; wherein said first and secondcrosslinkers have differing temperature responsive crosslinkingcharacteristics over the temperature range of about 70° F. to about 400°F. which enables crosslinking of said polymer and gelation of saidcomposition over substantially the entire temperature range.

According to other aspects of the invention, the composition is injectedinto a well and the surrounding formation, which preferably havetemperature conditions in the range of about 70° F. to about 175° F., tocause one of the crosslinkers to crosslink the polymer which results ingelation of the composition after its penetration into permeable zonesof the formation. Subsequently, steam is injected into the well andformation. Temperature conditions in the well and formation then raiseto higher temperature conditions in the range of about 175° F. to about400° F. so as to cause the other crosslinker to crosslink the polymerand preferably further harden the gel in the permeable thief zones ofthe formation.

According to a preferred embodiment, each of the crosslinkers comprise aphenolic compound and an aldehyde, and the water-dispersible polymerincludes an amide containing monomer. Utilizing the composition in steamtreatment of a well provides good penetration of the composition intothe formation as well as stability of the resulting gel when exposed tosteam temperatures for extended periods (i.e. up to several months).

DETAILED DESCRIPTION OF THE INVENTION

As noted above, the composition of the invention broadly compriseswater; a water-dispersible polymer; and two crosslinkers with differingtemperature responsive crosslinking characteristics over the temperaturerange of about 70° F. to about 400° F. One crosslinker can becharacterized as a "low temperature crosslinker", and the othercrosslinker can be characterized as a "high temperature crosslinker".Preferably, the low temperature crosslinker is effective in crosslinkingthe polymer in a temperature range of about 70° F. to about 175° F., andthe high temperature crosslinker is effective in crosslinking thepolymer in the range of about 175° F. to about 400° F. In the followingdetailed description of the inventive composition, the terms hightemperature crosslinker and low temperature crosslinker will continue tobe used for the sake of convenience to refer to the respectivecrosslinkers which are activated and effective at the above-mentionedtemperature ranges.

Further as used herein, the "water-dispersible" components of thecomposition include components which are truly water soluble and thosewhich are dispersible in water to form stable suspensions. Also as usedherein, the term "weight percent" is that percentage based on the totalweight of the composition.

With respect to the crosslinkers generally, any crosslinkers which willeffectively crosslink the polymer in the temperature ranges describedcan be employed. Desirably, such crosslinkers are stable at thetemperature and pressure conditions to which they are exposed in asubterranean formation. By use of the term "stable", this is intended tomean that the gel produced by a particular crosslinker retains itsviscosity and remains a homogenous, elastic mass which does not shrinkor expel water. It is preferred that the low temperature crosslinker isstable until steam is injected and the second high temperaturecrosslinker is activated by the temperature of the steam. One day toseveral days of stability is typically sufficient for this purpose. Itis preferred that the high temperature crosslinker be stable forsomewhat longer periods, for example several weeks or months, duringwhich time the steam is injected.

Preferred low temperature crosslinkers which exhibit highly effectivecrosslinking with water-dispersible polymers and which exhibit desirablestability characteristics include particular phenolic compounds, laterdescribed in detail, in combination with an aldehyde.

Any water-dispersible aldehyde can be utilized in the invention. Thus,suitable aldehydes can be selected from the group consisting ofaliphatic monoaldehydes, aromatic monoaldehydes, aliphatic dialdehydes,and aromatic dialdehydes. Preferred aldehydes can be selected from thegroup consisting of formaldehyde, paraformaldehyde, acetaldehyde,butyraldehyde, isobutyraldehyde, heptaldehyde, decanal, glyoxol,glutaraldehyde, and terephthaldehyde. Formaldehyde is presentlypreferred due to its effectiveness, ready availability and relativelylow expense.

Water-dispersible phenolic compounds suitable for use in the lowtemperature crosslinker can be characterized by the formula ##STR1##where each R is independently selected from: a hydroxyl group; an NR¹ R¹group having no more than 6 carbon atoms and where R¹ is selected fromhydrogen or an alkyl group; an alkoxy group having 1 to 6, preferably 1to 3, carbon atoms; an NHCOCH₃ group; an alkyl group having 1 to 6,preferably 1 to 2, carbon atoms; a phenyl group; and hydrogen; providedfurther that at least two of the R groups are hydrogens and at least oneof the remaining R groups is not a hydrogen. It is most preferred thatthe nonhydrogen functional groups selected from those above arepositioned at the number 3 and/or 5 meta position(s) of the phenolicring, but any combination of the functional groups can be at anypositions around the ring, provided as noted previously that at leasttwo of the functional R groups are hydrogens and at least one of theremaining R groups is not a hydrogen, and provided that the phenoliccompound is water-dispersible.

Specific examples of phenolic compounds useable with aldehyde as the lowtemperature crosslinker include resorcinol, catechol, phlorglucinol(1,3,5-trihydroxybenzene), pyrogallol (1,2,3-trihydroxybenzene),m-aminophenol, m-N-methylaminophenol, m-N-dimethylaminophenol,m-methoxyphenol, m-N-acetamidephenol, m-cresol, and m-phenylphenol.Resorcinol is the presently preferred low temperature phenolic compounddue to its effective crosslinking, stability characteristics, lowexpense and ready availability.

The phenolic compound of the low temperature crosslinker is present inthe composition in the range of about 0.01 to about 1.0 weight percentand more preferably in the range of about 0.03 to about 0.3 weightpercent. The aldehyde associated with the phenolic compound is presentin the composition in the range of about 0.025 to about 1 weight percentmost preferably in the range of about 0.03 to about 0.5 weight percent.

Other suitable low temperature crosslinkers include water-dispersiblecompound of a metallic cation selected from the group consisting ofCa²⁺, Mg²⁺, Al³⁺, Cr³⁺, Zn²⁺, Fe²⁺, Fe³⁺, Zr⁴⁺, Ti⁴⁺, Sn⁴⁺, wherein thecompound is activated and effective in crosslinking thewater-dispersible polymer at a temperature of about 70° F. to about 175°F.

The anion(s) associated with one of the above metallic cations ispreferably derived from a water-dispersible acid. Specific suitableanions include nitrate, chloride, ortho-phosphate, sulfate, perchlorate,carboxylates having 1 to 3 carbon atoms such as formate, acetate andpropionate, α-hydroxy carboxylates such as glycolate and α-hydroxypropionate, α-hydroxy tricarboxylates such as citrate, metaphosphate,nitrilotriacetate, tartrate, tripolyphosphate, and gluconate. Any one orcombination of the above anions can be associated with a metallic cationto form the low temperature crosslinking compound.

Specific examples of such low temperature crosslinking compounds includechromium chloride, chromium acetate, chromium propionate, aluminumcitrate, zirconium tetraacetate, zirconium chloride, zirconiumtetrachloride, ferric citrate, and zinc chloride. Such a low temperaturecrosslinking compound is generally present in the composition in theamount of about 0.005 to about 0.1 weight percent, most preferably inthe amount of about 0.01 to 0.05 weight percent.

Preferred water-dispersible high temperature crosslinkers includeparticular phenolic compounds, later described in detail, in combinationwith an aldehyde. The aldehyde can be any one of those previouslydescribed. If such a phenolic-aldehyde high temperature crosslinker isused with a phenolic-aldehyde low temperature crosslinker, the aldehydesof each crosslinker may be different aldehydes or the same aldehyde. Forexample, formaldehyde alone may be used in combination with low and hightemperature phenolics to make up both the low and high temperaturecrosslinkers.

Preferred water-dispersible phenolic compounds for use in the hightemperature crosslinker include those of the formula ##STR2## where eachR² is independently selected from one of the groups: NO₂ ; carboxyl;sulfonic acid; CHO; COR³ where R³ is an alkyl group having 1 to 6 carbonatoms, preferably only 1 carbon atom; a halogen such as F, Cl, Br or I;and hydrogen. Any combination of the above functional groups at variouspositions of the phenolic ring is possible, providing the phenoliccompound is water-dispersible.

Specific examples of water-dispersible phenolic compounds for use in thehigh temperature crosslinker include phenol (where each R² is hydrogen),nitrophenol, hydroxybenzoic acid, phenolsulfonic acid, bromophenol,chlorophenol, and dichlorophenol. Of the above compounds, phenol ispresently preferred.

The phenolic compound for use in the high temperature crosslinker can bepresent in the composition in the amount of about 0.02 to about 1 weightpercent, most preferably in the amount of about 0.05 to about 0.5 weightpercent. The aldehyde associated with the phenolic compound can bepresent in the amount of about 0.025 to about 1 weight percent, mostpreferably about 0.03 to about 0.5 weight percent.

Other suitable high temperature crosslinkers include water-dispersiblechelated complexes of a metallic ion selected from Zr⁴⁺, Ti^(4'), andCr³⁺ which effectively crosslink the water-dispersible polymer attemperatures of about 175° F. to about 400° F. As used herein a chelatedcomplex is a compound wherein a metallic ion is complexed with a ligandhaving more than one functional group bonded to the metallic ion.Chelation imparts additional stability to the complex and thus raisesthe crosslinking activation temperature.

Preferred chelated complexes include complexes of one of the abovemetallic cations with at least one β-diketone, where β-diketone has thegeneral formula ##STR3## where each R⁴ is an alkyl group, preferablyhaving 1 to 3 carbon atoms, and where each R⁵ is independently selectedfrom hydrogen or an alkyl group preferably having 1 to 3 carbon atoms,and provided further that at least one of the R⁵ groups is hydrogen. Anexample of a suitable β-diketone is acetylacetone. Specific examples ofcomplexes with β-diketones include titanium complexes such asdi-isopropoxy-bis-(2,4-pentandionato)titanium (IV), zirconium complexessuch as tetrakis-(2,4-pentandionato)-zirconium (IV) and chromiumcomplexes such as tris-(2,4-pentandionato)chromium (III).

Other chelated complexes suitable for use as the high temperaturecrosslinkers include complexes of one of the metallic cations with analkanolamine. Specific examples of such alkanolamines includeethanolamine and triethanolamine. Specific examples of such complexesinclude di-propoxy-bis-triethanolamine titanate (IV) anddi-isopropyl-bis-triethanolamine-titanate (triethanolamine titanate).

A high temperature crosslinking compound of one of the above metalliccations is generally present in the composition in the range of about0.005 to about 0.1 weight percent, most preferably in the range of about0.01 to about 0.05 weight percent.

It should be understood that the above described preferred high and lowtemperature crosslinkers can be combined in any combination. Forexample, a phenolic-aldehyde crosslinking can be combined with ametallic type crosslinker, or each crosslinker may be of thephenol-aldehyde type, or each crosslinker may be of the metallic type.

It is presently preferred to utilize phenolic-aldehyde type high and lowtemperature crosslinkers. The most preferred crosslinking systemincludes resorcinol, phenol and formaldehyde. The resorcinol and phenolare preferably present in amounts like those cited above with respect tothe description of the two types of phenolic compounds, and theformaldehyde is preferably present in the amount of about 0.05 to about2 weight percent. It has been found that this crosslinking system giveshighly effective gelation of the composition and provides excellentstability. Furthermore the components are readily available andrelatively inexpensive.

Preferred water-dispersible polymer for use with the present inventioninclude polymers containing a monomer with an amide functional group.Such a monomer can be expressed by the formula ##STR4## where each R⁶ isselected from a hydrogen and an alkyl group having from 1 to 3 carbonatoms.

Polymers including a monomer as defined above are particularly preferredwhen used in conjunction with at least one phenolic-aldehyde crosslinkerdue to the highly effective crosslinking obtained with such acrosslinker-polymer combination.

Suitable polymers which include the above described monomer arehomopolymers of such monomers, and copolymers of such a monomer with anyethylenically unsaturated monomer from the group consisting of acrylicacid, methacrylic acid, vinylsuflonic acid, vinylbenzylsulfonic acid,vinyl acetate, acrylonitrile, methyl acrylonitrile, vinyl alkyl ether,vinyl chloride, maleic anhydride, vinyl substituted cationic quaternaryammonium compounds, 2-acrylamido-2-methyl-propane sulfonic acid, sodium2-acrylamido-2-methylpropane sulfonate, and vinyl pyrrolidone.

Particularly preferred water-dispersible polymers of the presentinvention can be selected from the group consisting of homopolymers ofacrylamide, copolymers of acrylamide and vinyl pyrrolidone, homopolymersof methacrylamide, copolymers of acrylamide and methacrylamide,copolymers of acrylamide and acrylic acid, copolymers of methacrylamide,and acrylic acid, terpolymers of vinyl pyrrolidone, acrylamide andsodium 2-acrylamido-2-methylpropane sulfonate, and copolymers ofacrylamide and sodium 2-acrylamido-2-methylpropane sulfonate.

The relative ratios of the monomers are not critical to the practice ofthe present invention. However, specific preferred polymers include: a60:40 weight percent copolymer of vinyl pyrrolidone and acrylamide; a50:50 weight percent copolymer of vinyl pyrrolidone and acrylamide; a30:15:55 weight percent terpolymer of vinyl pyrrolidone, acrylamide, andsodium 2-acrylamido-2-methylpropane sulfonate; a 40:60 weight percentcopolymer of acrylamide and sodium 2-acrylamido-2-methylpropanesulfonate; and homopolymers of acrylamide wherein not more than about40% of the carboxyamide groups are hydrolyzed.

Other suitable but less preferred water-dispersible polymers includepolysaccharides like cellulose ethers. Examples of such cellulose ethersinclude various carboxy-alkyl cellulose ethers such as carboxyethylcellulose and carboxymethyl cellulose (CMC), and mixed ether such ascarboxyalkyl hydroxyalkyl etnhers. The class of polymers referred toabove as polysaccharides encompasses biopolysaccharides which arebiochemically produced by the action of bacteria upon sugar, starches,and similar carbohydrates.

The water-dispersible polymer used in the composition can take anysuitable form such as gel-log (a semi-solid containing about 50 to about75 weight percent water), a powder, a solution, an inverse water-in oilemulsion, etc.

The molecular weights of the water-dispersible polymers used in thepresent invention is not critical. It is preferred however that thepolymer have a molecular weight of between 100,000 and 20,000,000. Theupper limit of molecular weight is unimportant so long as the polymer isstill water-dispersible and can be pumped into a formation.

The polymer, particularly with respect to acrylamide polymers, ispresent in the composition in the amount of about 0.05 to about 10weight percent, preferably about 0.2 to about 4 weight percent. Theconcentration of polymer in the composition depends to some degree uponthe molecular weight of the polymer. A high molecular weight results ina higher viscosity of the resulting gel for a particular concentrationof polymer.

The manner in which the water-dispersible polymer is polymerized is notcritical to the practice of the present invention. Polymerization can beinitiated by chemicals, radiation, or any other technique known to thoseskilled in the art.

Any suitable method can be employed for preparing the composition of theinvention. Thus, any suitable mixing technique or order of addition ofthe components of the composition to each other can be employed.However, the polymer should be dispersed in water before contacting thepolymer with the other components. The mixing order can vary with thetype of polymer used.

The composition of the invention can be used in steam treatment of asubterranean formation by injecting the composition into a well whichpenetrates the formation. The steam treatment method of the inventionwill be described in terms of a cyclic operation wherein the same wellis used to inject the steam and produce the oil. Of course, thecomposition of the invention can be used with other types of steamtreatment.

First, the composition is injected into the well, preferably when thewell is cold, that is in the temperature range of about 70° F. to about175° F. and most typically at the lower end of this range. The well andsurrounding formation preferably remain in this temperature range duringand immediately after the composition injection and until thecommencement of steam injection. After injection of the composition iscomplete, it is typical to shut in the well for a few days and allow thecomposition to properly set up to a gel in the permeable thief zones ofthe formation. It should be apparent that it is advantageous to delaythe gelation of the composition to permit injection of larger volumes ofthe composition into the formation and thereby block thief zones thatwould normally go untreated due to their distance from the injectionsite. The composition of the invention using low temperaturecrosslinkers described above enables excellent penetration into theformation because of a relatively slow rate of gelation, as is shown byexamples later described.

Next, steam is injected into the well. Such injection can continue forseveral days to several weeks during which time, and immediatelythereafter, the temperature of the formation is generally maintained attemperature conditions (i.e. 175° F. to 400° F.) which cause the hightemperature crosslinker to effectively crosslink the water-dispersiblepolymer and to preferably further harden the gel in the permeable thiefzones of the formation. It has been found that crosslinking the polymerwith the low temperature crosslinker followed by crosslinking thepolymer with the high temperature crosslinker produces in most cases aharder and a longer lasting gel which can withstand the temperatures ofthe steam for much longer periods than prior art treatments, such asfoam treatments. Therefore, blockage of the thief zones is optimized tothereby maximize oil recovery.

After injection of the steam is completed, the well is again shut in andthe steam allowed to "soak" for several days. Production can then beginwherein a mixture of water and oil is produced by the well. Conventionalequipment is used to separate the oil from the water. In such a cyclicoperation, the above steps can be repeated wherein composition and steamare injected into the well, followed by production of oil and water fromthe well.

As noted previously, the composition of the invention can be used inconjunction with other types of steam treatment. For example, in a"steam drive" operation, cooling water can be injected into the well tocool the well to the desired temperature range after a previous steamtreatment. The composition can then be injected as explained above.

Several examples will now be described which should not be construed tolimit the invention in any manner.

Some of the examples use a qualitative measurement herein called "gelstrength", which is in terms of a percentage. Gel strength for aparticular sample is obtained as follows: 20 ml of a pre-gel solution ofpolymer and crosslinkers are placed in a 23 mm O.D.×225 mm long ampule.The ampule is sealed under anerobic conditions and aged in the verticalposition in an oven for the desired period of time at the desiredtemperature. After the specified time elapses, the ampule is taken outof the oven and laid horizontally on a graduated scale. If the solutionspreads along the whole ampule, then the gel strength is zero and thesolution did not gel. If the gel is strong and does not flow, i.e., itslength is exactly the same as that of the pre-gel solution, then the gelstrength is 100%. Any gel strength in between these two extremes iscalculated from the formula:

    (AL-TL)/AL×100

where AL is the ampule length (225 mm) and TL is tongue length of thegel measured on the scale in mm. Tongue length is defined as the lengthof that portion of the gel within the horizontally disposed ampule whichextends beyond the point at which the gel contacts the interior surfaceof the ampule around the entire circumference of the ampule, after theampule is horizontal for 1 to 2 minutes.

EXAMPLE I

The purpose of this example is to demonstrate the temperature dependentcrosslinking characteristics of a phenol/formaldehyde crosslinkingsystem.

A 0.5 weight percent solution of a polymer composed of 50 parts byweight vinylpyrrolidone (VP) and 50 parts by weight acrylamide (AM) wasprepared by dissolving 16.67 grams of a gel-log containing 30 weightpercent active polymer in 983.33 ml of water. This solution was leftovernight to ensure total hydration of the polymer.

The solution was divided into five 200 ml portions. 0.713 ml (measuredwith a microsyringe) of an aqueous solution containing 26.4 weightpercent phenol and 25.9 weight percent formaldehyde was added to andmixed thoroughly with one such 200 ml polymer solution. The resultingsolution contained 0.5 weight percent polymer, 0.1 weight percent phenoland 0.1 weight percent formaldehyde. 20 ml of this solution was placedin each of ten glass ampules having dimensions as described previously.The ampules were purged with nitrogen and selected. Two ampules wereplaced vertically in each of five ovens set at 130° F., 175° F., 200°F., 250° F. and 300° F. respectively. The ampules were removed from theovens periodically, the gel strengths measured, and the time (in days)after commencemenet of heating recorded. After each gel strengthmeasurement, the ampules were returned to the ovens in a verticalposition. Gel strengths measured for each pair of ampules correspondingto a particular oven were averaged to give gel strengths for the varioustemperatures and time periods as is shown in Table I.

                  TABLE I                                                         ______________________________________                                        Time   Gel Strength (%) at Various Temperatures                               (Days) 130° F.                                                                          175° F.                                                                        200° F.                                                                        250° F.                                                                      300° F.                         ______________________________________                                        1      0          0       0      58    98                                     3      0          0       0      97    81                                     13     0          0      89      98    73                                     31     0         55      97      93    63                                     62     0         58      100     96    63                                     94     0         88      100     93    65                                     141    65        98      97      95    67                                     219    66        98      97      94    90                                     ______________________________________                                    

At 130° F., well over 100 days are required for crosslinking andconsequent gelation. The time required for gelation decreases withincreasing temperatures. Note in particular that at temperatures of 250°F. and 300° F., the composition gels to desirably high gel strengthsafter only 1 day of heating. Such temperature conditions are typical ina subterranean formation after steam treatment. Note also that as thehigher temperature of 175° F. and above, the gel is extremely stable andin most cases actually increases in gel strength as time of heatingprogresses. The data therefore illustrates the suitability ofphenol-formaldehyde as a high temperature crosslinker.

EXAMPLE II

The purpose of this example is to demonstrate the temperature dependentcrosslinking characteristics of a resorcinol-formaldehyde crosslinkingsystem.

350 ml of polymer solution was prepared using the same polymer type,concentration and preparative procedure as described in Example I. 5.46ml of an aqueous resorcinol solution containing 5.13 weight percentresorcinol, and 16 ml of an aqueous formaldehyde solution containing 4.2weight percent formaldehyde were added to, and mixed thoroughly with,the polymer solution. The resulting solution therefore contained 0.5weight percent polymer, 0.08 weight percent resorcinol and 0.2 weightpercent formaldehyde.

20 ml of this solution was placed in each of sixteen ampules, which werethen purged and sealed as described in Example I. Two ampules wereplaced in each of eight ovens set at 104° F., 120° F., 130° F., 150° F.,175° F., 200° F., 250° F. and 300° F. respectively. Gel strengths atvarious times were measured and averaged as in Example I. These resultsare shown in Table II.

                  TABLE II                                                        ______________________________________                                        Gel Strength (%) at Various Temperatures                                      Time  104°                                                                          120°                                                                           130°                                                                        150°                                                                         175°                                                                        200°                                                                         250°                                                                        300°                   (Days)                                                                              F.     F.      F.   F.    F.   F.    F.   F.                            ______________________________________                                        .08    0      0       0    0     0   13    0    0                             1     35     51      37   40    35   26    0    0                             4     41     35      42   40    24   24    0    0                             14    70     36      39   37    32   27    0    0                             42    40     36      31   53    40   24    0    0                             64    40     35      41   50    40   28    0    0                             77    36     41      33   52    40   29    0    0                             ______________________________________                                    

It can be seen that no gelation occurs through 77 days at 250° F. or300° F., indicating that resorcinol-formaldehyde substantially fails tocrosslink the polymer after exposure to these temperatures for theindicated time periods. Even at 200° F., Table II shows a generaldecrease in gel strengths from those obtained at 175° F. The suitabilityof resorcinol-formaldehyde as a low temperature crosslinker should beapparent from this data.

EXAMPLE III

The purpose of this example is to demonstrate the desirable response ofgelable polymer compositions to a resorcinol-phenol-formaldehydecrosslinking system.

1200 ml of polymer solution was prepared using the same polymer type,concentration and preparative procedure as described in Example I. Thepolymer solution was divided into three 400 ml portions. 5 ml of anaqueous solution containing 5.13 weight percent resorcinol was added toone 400 ml polymer solution portion. 7.5 and 10 ml of the 5.13 percentresorcinol solution were added to the second and third 400 ml portionsrespectively. The three resulting solutions contained 0.0611, 0.0916 and0.1222 weight percent resorcinol, respectively.

Each of the three solutions was subdivided into five 80 ml portions. Tothe five portions were added, respectively, 0.213, 0.284, 0.426, 0.568,and 0.710 ml of the 26.4% phenol and 25.9% formaldehyde solutiondescribed in Example I. The resulting phenol/formaldehyde weight percentvalues were, respectively, 0.075/0.075, 0.100/0.100, 0.150/0.150,0.200/0.200 and 0.250/0.250. Therefore, fifteen solutions resultingwhich included three sets of five solutions, wherein each setcorresponded to one of the respective resorcinol concentrations (0.0611,0.0916 and 0.1222 weight percent) and the respective five differentphenol/formaldehyde concentrations.

Each of the fifteen solutions was divided equally between four ampuleswhich were purged with nitrogen and sealed. Two ampules were placed inan oven set at 120° F. to test the low temperature response of thecomposition over an extended period. The other two ampules were placedin another oven set at 130° F. One of the ampules was removed andtransferred to a 300° F. oven. No data is presented for the one ampulewhich remained in the 130° F. oven since the solution therein behavedsimilarly to the solutions in the 120° F. oven.

Table IIIA sets forth gel strengths at various times which were obtainedby heating five pairs of ampules at 120° F. Gel strengths for each pairwere averaged as described previously. The ampule solutions all had0.0611 weight percent resorcinol but varying concentrations ofphenol/formaldehyde.

                  TABLE IIIA                                                      ______________________________________                                        Gelation at 120° F. With .0611 wt. % Resorcinol                              Gel Strength (%) at Various                                             Time  Phenol/Formaldehyde wt. %'s                                             (Days)                                                                              .075/.075                                                                              .100/.100 .155/.155                                                                            .200/.200                                                                             .250/.250                             ______________________________________                                        1      0        0        10     24      26                                    4     20       31        33     49      50                                    8     24       39        48     53      62                                    28    30       44        46     56      57                                    40    37       37        56     62      45                                    62    26       33        41     49      37                                    78    26       38        46     45      57                                    ______________________________________                                    

It can be readily seen from Table IIIA that the solutions gel slowly,particularly for the phenol/formaldehyde concentrations of 0.075/0.075and 0.100/0.100 weight percent. Note for these concentrations, the gelstrength was 0 after 1 day. However, the gels formed are relativelyweak, particularly at the 0.075/0.075 weight percent phenol/formaldehydeconcentrations.

Table IIIB sets forth gel strengths obtained in a manner similar tothose obtained in Table IIIA except with a resorcinol concentration of0.0916 weight percent resorcinol.

                  TABLE IIIB                                                      ______________________________________                                        Gelation at 120° F. With .0916 wt. % Resorcinol                              Gel Strength (%) at Various                                             Time  Phenol/Formaldehyde wt. %'s                                             (Days)                                                                              .075/.075                                                                              .100/.100 .150/.150                                                                            .200/.200                                                                             .250/.250                             ______________________________________                                        .167   0        0         0      0       0                                    3     61       66        69     72      72                                    5     61       76        74     72      71                                    7     57       47        73     74      76                                    27    32       37        69     38      51                                    41    23       31        28     34      36                                    61    31       31        33     34      36                                    77    31       34        36     35      46                                    ______________________________________                                    

A comparison of Tables IIIA and IIIB indicates a generally faster rateof gelation with 0.0916 weight percent resorcinol than with 0.0611weight percent resorcinol. However Table IIIB does show the gelstrengths to be 0 in every case at 0.167 days, thus indicating somedelay in gelation. Further, the data of Table IIIB indicates the gelsformed after several days are stronger than those formed with 0.0611weight percent resorcinol.

Table IIIC sets forth gel strengths obtained at 120° F. for a resorcinolconcentration of 0.1222 weight percent.

                  TABLE IIIC                                                      ______________________________________                                        Gelation at 120° F. With .1222 wt. % Resorcinol                              Gel Strength (%) at Various                                             Time  Phenol/Formaldehyde wt. %'s                                             (Days)                                                                              .075/.075                                                                              .100/.100 .150/.150                                                                            .200/.200                                                                             .250/.250                             ______________________________________                                        .75    0        0        48     66      72                                    2     59       63        76     81      80                                    3     61       59        81     75      58                                    4     52       40        61     62      55                                    24    28       28        38     38      35                                    38    27       31        34     32      29                                    58    19       27        29     30      31                                    74    18       22        27     32      28                                    ______________________________________                                    

Table IIIC indicates significant delay in gelation at the lowerphenol/formaldehyde concentrations and gelation to a strong gel afteronly 2 days for all phenol/formaldehyde concentrations.

To summarize the data of Tables IIIA, IIIB and IIIC, the datacollectively indicates the resorcinol, phenol and formaldehydecrosslinking system to be effective in delayed gelation of the solutionsto acceptable strong gels at 120° F. This is desirable in a steamtreatment operation, since the solutions injected into a "cold"underground formation should effectively penetrate the formation beforegelation and then form acceptably strong gels.

As noted previously, half (thirty) of the originally prepared ampuleswere placed in a 130° F. oven. After ten days of "aging" in the 130° F.oven five "duplicate" (an ampule of a pair of ampules) ampules having0.0916 weight percent resorcinol and five duplicate ampules having0.1222 weight percent resorcinol were removed from the oven. After 11days of 130° F. aging five duplicate ampules having 0.0611 weightpercent resorcinol were removed from the oven. After removal from the130° F. oven, the ampules were placed in a 300° F. oven to test for thegelation response of the solutions to conditions comparable to steamtreatment conditions. The following Tables IIID, IIIE and IIIF set forthgel strength measured for the 0.0611%, 0.0916% and 0.1222% resorcinolampules respectively. Note that only one ampule of each ampule pair wastransferred to the 300° F. oven, so that the gel strengths given in thefollowing Tables are not averaged values as were obtained in TablesIIIA, IIIB and IIIC.

                  TABLE IIID                                                      ______________________________________                                        Gelation at 300° F. With .0611 wt. % Resorcinol Solution               Aged 11 Days at 130° F. Prior to Aging at 300° F.                     Gel Strength (%) at Various                                             Time  Phenol/Formaldehyde wt. %'s                                             (Days)                                                                              .075/.075                                                                              .100/.100 .150/.150                                                                            .200/.200                                                                             .250/.250                             ______________________________________                                        3      0       41        59     80      79                                    10    15       41        64     69      75                                    18    22       67        49     64      76                                    25    22       49        47     53      57                                    31    32       44        50     58      48                                    51    44       68        52     57      88                                    67    31       40        48     59      53                                    88    29       31        48     56      49                                    115   27       25        46     48      50                                    170    0        0        40     44      45                                    ______________________________________                                    

                  TABLE IIIE                                                      ______________________________________                                        Gelation at 300° F. With .0916 wt. % Resorcinol Solution               Aged 10 Days at 130° F. Prior to Aging at 300° F.                     Gel Strength (%) at Various                                             Time  Phenol/Formaldehyde wt. %'s                                             (Days)                                                                              .075/.075                                                                              .100/.100 .150/.150                                                                            .200/.200                                                                             .250/.250                             ______________________________________                                        3     19       32        43     48      91                                    10    20       27        47     44      84                                    18    31       26        78     47      69                                    25    29       29        76     46      54                                    31    29       32        75     49      52                                    51    72       35        86     56      58                                    67    78       60        44     84      56                                    88    72       36        45     45      56                                    115   44       36        57     41      45                                    170   44       36        43     46      82                                    ______________________________________                                    

                  TABLE IIIF                                                      ______________________________________                                        Gelation at 300° F. With .1222 wt. % Resorcinol Solution               Aged 10 Days at 130° F. Prior to Aging at 300° F.                     Gel Strength (%) at Various                                             Time  Phenol/Formaldehyde wt. %'s                                             (Days)                                                                              .075/.075                                                                              .100/.100 .150/.150                                                                            .200/.200                                                                             .250/.250                             ______________________________________                                        7      3       26        32     37      50                                    15    33       39        36     60      74                                    22    39       37        43     44      50                                    28    68       53        83     50      76                                    51    52       70        88     47      88                                    67    75       87        77     50      56                                    88    52       82        67     88      52                                    115   46       61        39     88      44                                    170   54       52        42     49      47                                    ______________________________________                                    

Generally, the data of Tables IIID, IIIE and IIIF indicate that thesolutions generally have relatively high gel strengths after exposure to300° F. for several days. It is important to note that these aretemperature conditions encountered in steam treatment. In many cases,the gel actually hardens on continued exposure to the 300° F.conditions. Most importantly, the data shows the gels to be stablethrough 115 days of treatment in every case. Except for two of thelowest phenol/formaldehyde concentrations at a 0.0611 weight percentresorcinol concentration, all gels remainded stable through 170 days oftreatment.

The data of Example III therefore clearly shows that solutions inaccordance with the invention effectively gel at low temperatures below175° F., and that gels so formed can withstand temperature conditionsassociated with well steam treatments for an extended period of time.

EXAMPLE IV

The purpose of this example is to demonstrate that a well treated with acomposition in accordance with the invention effectively blockspermeable zones of a formation so that injected steam is necessarilydiverted to other zones of the formation.

An aqueous solution was prepared containing 1 weight percent 50:50vinylpyrrolidone/acrylamide copolymer, 0.4 weight percent phenol, 0.4weight percent formaldehyde and 0.16 weight percent resorcinol. Thetreated well has casing and tubing which extends to respective depths ofabout 1120 feet and 1240 feet respectively. The well has 160 feet ofopen sandface. Solution was injected into the well for a period of about18.5 hours. The well received a total of 2399 pounds of polymer, 381pounds of resorcinol, 844 pounds of phenol and 897 pounds offormaldehyde. The well was then shut in for four days, after which steamwarming was carried out for about twelve hours. Full steam injection wasthen started. A total of 6181 barrels of steam were injected in thiscycle, denoted as cycle A, of a cyclic type operation. Steam injectionrates and pressures are shown in Table IVA.

                  TABLE IVA                                                       ______________________________________                                        Cycle A                                                                                                    Casing  Tubing                                         Steam Rate             Pressure                                                                              Pressure                                 Day   (bbl/hr)               (psi)   (psi)                                    ______________________________________                                        1     26                       660     780                                    2     27                       620     1000                                   3     35                       800     950                                    4     32                       880     860                                    5     58                       800     840                                    6     51                       740     840                                    7     53                       740     840                                          Total: 6181                                                                             bbl    Average:                                                                              748     878                                    ______________________________________                                    

The following Table IVB shows the steam pressures and injection ratesfor the cycle, denoted as cycle B, immediately preceding Cycle A. Nogelable compositions were injected into the well in conjunction withcycle B.

                  TABLE IVB                                                       ______________________________________                                        Cycle B                                                                                      Casing   Tubing                                                               Pressure Pressure                                              Day            (psi)    (psi)                                                 ______________________________________                                        1              250      240                                                   2              215      240                                                   3              120      220                                                   4              110      200                                                   5              110      200                                                   Average:       161      220                                                   ______________________________________                                    

By comparing the pressures of Table IVA and IVB, it can be determinedthat the steam injection pressures through the tubing and the casing inCycle A were 4.0 and 4.7 times those in Cycle B. This definitelyindicates that the injected gelable composition associated with Cycle Asuccessfully gelled in various zones in the formation to createresistance to steam flow into these zones, thereby diverting steam toother less permeable zones.

Even though the composition of the invention was shown to effectivelygel and withstand steam temperature conditions during steam injection,production of water and oil decreased from that obtained in Cycle B.Through analysis of injection profiles, it was determined that the steaminjected in Cycle A went mainly into ratty sand (shaly sands and/orthinly interbedded sands and shales), which is expected to contain lessoil than clean sand. It appears probable that the steam was injected inCycle A at pressures larger than the fracturing pressure, and when thewell was put on production the fractured ratty sand closed up preventingany stimulated oil from reaching the wellbore. This indicates to thoseskilled in the art of well treatment that this well was overtreated andthat more successful results would be achieved through injecting smallervolumes of the gelable composition, which would seal off less of theproductive sands.

Obviously many modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

That which is claimed is:
 1. A method of treating a subterranean formation penetrated by a well comprising:(a) injecting a gelable composition into the well wherein the composition consists essentially of water, a water-dispersible polymer, a first water-dispersible crosslinker, and a second water-dispersible crosslinker wherein said first and second crosslinkers have differing temperature responsive crosslinking characteristics over the temperature range of about 70° F. to about 400° F. which enables crosslinking of said polymer and gelation of said composition over substantially the entire temperature range of about 70° F. to about 400° F.; and (b) injecting steam into the well after step (a).
 2. A method in accordance with claim 1 wherein the composition in step (a) penetrates into certain zones of the formation and wherein the composition after its injection is allowed to set in the formation for a predetermined period of time before commencement of step (b).
 3. A method in according with claim 1 wherein the first crosslinker is selected froma first water-dispersible phenolic compound and a water-dispersible aldehyde; a compound of a metallic cation selected from the group consisting of Ca²⁺, Mg²⁺, Al³⁺, Cr³⁺, Zn²⁺, Fe²⁺, Fe³⁺, Zr⁴⁺, Ti⁴⁺ and Sn⁴⁺.
 4. A method in accordance with claim 3 wherein the second crosslinker is selected froma second water-dispersible phenolic compound and a water-dispersible aldehyde; a chelated complex of a metallic cation selected from the group consisting of Zr⁴⁺, Ti⁴⁺ and Cr³⁺.
 5. A method in accordance with claim 4 wherein the first crosslinker comprises the first phenolic compound and aldehyde and wherein the second crosslinker comprises the second phenolic compound and aldehyde, and wherein the polymer contains a monomer having the formula ##STR5## where each R⁶ is selected from a hydrogen and an alkyl group having 1 to 3 carbon atoms.
 6. A method in accordance with claim 5, wherein said first phenolic compound has the general formula ##STR6## wherein each R group is independently selected from a hydroxyl group, an NR¹ R¹ group having 1 to 6 carbon atoms where R¹ is hydrogen or an alkyl group, an alkoxy group having 1 to 6 carbon atoms, an NHCOCH₃ group, an alkyl group having 1 to 6 carbon atoms, a phenyl group, and hydrogen, provided that at least two of the R groups are hydrogens and at least one of the remaining R groups is not a hydrogen.
 7. A method in accordance with claim 6 wherein said second phenolic compound has the general formula ##STR7## wherein each R² is independently selected from NO₂, a carboxyl group, sulfonic acid, CHO, COR³ where R³ is an alkyl group having 1 to 6 carbon atoms, a halogen and hydrogen.
 8. A method in accordance with claim 1 wherein during and immediately after step (a) and until the commencement of step (b) temperature conditions in the formation are generally in the range of 70° F. to about 175° F. such that the first crosslinker crosslinks the polymer to thus gel the composition after its penetration into permeable zones of the formation.
 9. A method in accordance with claim 8 wherein during and immediately after step (b) the temperature conditions in the formation are maintained substantially in the range of about 175° F. to about 400° F. to cause the second crosslinker to crosslink the polymer and continue gelation of the composition in said permeable zones of the formation.
 10. A method in accordance with claim 5 wherein the amount of said water-dispersible polymer is in the range of about 0.05 to about 10 weight percent, wherein the amount of the first phenolic compound is in the range of about 0.01 to about 1 weight percent, wherein the amount of second phenolic compound is in the range of about 0.02 to about 1 weight percent, and wherein the amount of aldehyde is in the range of about 0.05 to about 2 weight percent.
 11. A method in accordance with claim 7 wherein said first phenolic compound is resorcinol and said second phenolic compound is phenol.
 12. A method of treating a subterranean formation penetrated by a well consisting of:(a) injecting a gelable composition into the well wherein the composition consists of water, a water-dispersible polymer, a first water-dispersible crosslinker, and a second water-dispersible crosslinker wherein said first and second crosslinkers have different temperature responsive crosslinking characteristics over the temperature range of about 70° F. to about 400° F. which enables crosslinking of said polymer and gelation of said composition over substantially the entire temperature range of about 70° F. to about 400° F.; and (b) injecting steam into the well after step (a).
 13. A method in accordance with claim 12 wherein said first crosslinker comprises resorcinol and a water-dispersible aldehyde and wherein said second crosslinker comprises phenol and a water-dispersible aldehyde. 